Computing normals using the HDK

[aaweb]

Hello there

I posted this on the SESI forums already, I hope that's ok (I'm aware some people check both).

I am working on integrating an FRep Library into Houdini using the HDK. I can output the mesh just fine, but there is still some artefacts because of missing normals. When trying to set the normals to a mesh, it doesn't seem to make a difference. Here's my code:

    
    GEO_PrimPoly *prim_poly_ptr;
    GEO_Point* added_points[vertexCount];

    // Add new points to the gdp. This is optional - you can also
    // reuse existing points and add them to the polygon instead.
    for(unsigned int point_idx = 0; point_idx < vertexCount; point_idx++)
    {
        // Append a new point
        added_points[point_idx] = gdp->appendPoint();
        // Set its coordinates
        added_points[point_idx]->getPos().assign( polygonizer.getVertex(point_idx).x,
                                                  polygonizer.getVertex(point_idx).y,
                                                  polygonizer.getVertex(point_idx).z
                                                  );

        VECTOR<BASIC_TYPE> tmpNormal = polygonizer.getNormal(point_idx);
        UT_Vector3 nml(tmpNormal.X, tmpNormal.Y, tmpNormal.Z);
        gdp->computeNormal(*added_points[point_idx], nml );
    }

    // Create a primitive for every face and append
    for (unsigned int i = 0; i < faceCount; i++)
    {
       // Append a new polygon primitive. Primitive types are defined in GEO_PrimType.h
       prim_poly_ptr = dynamic_cast<GEO_PrimPoly *>(gdp->appendPrimitive(GEOPRIMPOLY));
       prim_poly_ptr->setSize(0);

       // Append vertices that form this primitive
       prim_poly_ptr->appendVertex(added_points[polygonizer.getFace(i*3)]);
       prim_poly_ptr->appendVertex(added_points[polygonizer.getFace(i*3+1)]);
       prim_poly_ptr->appendVertex(added_points[polygonizer.getFace(i*3+2)]);

       // Close the primitive to make it a polygon instead of a polyline.
       prim_poly_ptr->close();
    }
    // ----------------------------------------

Do I have to tell Houdini somehow that I am providing vertex normals? Or invoking calculation of face normals?

Help is greatly appreciated

Andy

[edward]

computeNormal() will calculate an average normal from the adjacent polygons, it does _not_ set the normal. Normals are just vector attributes in the HDK and you manipulate them as such. So you do something like addNormalAttribute(GEO_POINT_DICT) and then set your normals using the returned attribute ref. See: http://www.sidefx.co...attributes.html

// untested
GB_AttributeRef normal_attrib = gdp->addNormalAttribute(GEO_POINT_DICT);
for (int i = 0; i < vertexCount; i++)
{
 VECTOR<BASIC_TYPE> tmpN = polygonizer.getNormal(i);
 added_points[i]->setValue<UT_Vector3>(normal_attrib, UT_Vector3(tmpN.X, tmpN.Y, tmpN.Z));
}

[aaweb]

computeNormal() will calculate an average normal from the adjacent polygons, it does _not_ set the normal. Normals are just vector attributes in the HDK and you manipulate them as such. So you do something like addNormalAttribute(GEO_POINT_DICT) and then set your normals using the returned attribute ref. See: http://www.sidefx.co...attributes.html

// untested
GB_AttributeRef normal_attrib = gdp->addNormalAttribute(GEO_POINT_DICT);
for (int i = 0; i < vertexCount; i++)
{
 VECTOR<BASIC_TYPE> tmpN = polygonizer.getNormal(i);
 added_points[i]->setValue<UT_Vector3>(normal_attrib, UT_Vector3(tmpN.X, tmpN.Y, tmpN.Z));
}

Great, edward. That did the trick Thank you!